1. Field of the Invention
The invention relates to micro-structures which are typically found in semiconductor devices and other minute devices such as resonant sensors or micromachines. More particularly, the invention relates to a method of liquid treatment of micro-structures comprising structural members liable to be bent during the process of the liquid treatment, and to micro-structures having structural members able to withstand permanent bend through the liquid treatment thereof. By way of example, such a micro-structure is often found in a capacitor of a semiconductor device called DRAM, in which the micro-structure is made up of structural members in the form of, e.g., a thin sheet, one end of which is fixed and the other end is free.
2. Description of Related Art
In capacitors of DRAM semiconductor devices referred to above, since the capacitors are required to have a certain capacity in very small, limited regions, the required capacitor areas can be secured by incorporating a three-dimensional construction such as a finned structure. Other minute devices, which are exemplified by resonant sensors and micromachines and made by applying processes used in the production of fine semiconductor devices, may employ micro-structures having members liable to be bent, such as fine beams or sheets, supported at one end or both ends thereof.
By way of example, a three-dimensional capacitor of a DRAM semiconductor device is illustrated in FIG. 1. In this drawing, 1 represents a semiconductor substrate, 2 and 3 are capacitor electrodes, and 4 is an insulating film. This capacitor is produced by the following procedure:
First, as shown in FIG. 2A, a first insulator film 11, a conductor film 12 for forming a horizontal electrode of the capacitor, and a second insulator film 11' are sequentially laminated on a semiconductor substrate 10. The insulator films 11 and 11' are formed by, e.g., chemical vapor deposition (CVD) of SiO.sub.2, and the conductor film 12 is made by, e.g., CVD of polysilicon. Subsequently, holes are made in the laminated films so as to expose the surface of the substrate 10 at the bottoms of the holes, and a film of conductor 13 (polysilicon in this explanation) is then deposited, as shown in FIG. 2B. Inside the holes, the deposited polysilicon is connected to the former polysilicon film 12, and will support a horizontal electrode later formed from the film 12. The laminated films are then etched so as to leave separate, respective portions around the holes on the substrate, to thereby provide separate capacitor portions, as shown in FIG. 2C. Thereafter, the remaining insulator films 11 and 11' are etched and removed, while micro-structures 14 are left which form one of the capacitor electrodes, one end of which is fixed at the central support and the other is free. A thin film of silicon nitride is then formed by CVD to provide an insulator film 15 for the capacitor, as shown in FIG. 2D. Finally, a polysilicon film is formed to provide opposite electrodes, to thereby complete a capacitor of three-dimensional structure as shown in FIG. 1.
During the sequential manufacturing processes described above, liquids, such as an enchant solution and water, are used for the etching of the insulator films 11 and 11' and the pretreatment (i.e., washing) for the subsequent formation of silicon nitride film 15. Conventionally, in these treatments using liquids, the substrate bearing materials for the production of capacitor is immersed in the liquid, and then removed therefrom at atmospheric pressure. To the inventors, knowledge, it is not known in the art to use an environment of a pressure less than atmospheric pressure to which a substrate is removed from a treating liquid, as in the present invention.
When the micro-structure of one of the electrodes for capacitor as indicated by 14 in FIG. 2D is investigated after the etching of the laminated films for the formation of the separate capacitor portions (FIG. 2C), followed by the removal of the insulator film, a phenomenon may be observed in which the free end of a fin-like electrode 22 projecting from the support 21 is bent, and is in contact with the free end of another electrode 22 or the substrate 20, as shown in FIG. 3. The phenomenon will become more common as finer capacitors are made and the space between the fins and the thickness of the fins are accordingly reduced. In most cases, such a fin-like member brought into contact with another member or the substrate, will not be separated from the opposite member or substrate, that is, such a member will remain deformed. The bend and contact of the fin-like member with another member or substrate lead to the decrease in capacitor areas, and should therefore be eliminated.
Also, in resonant sensors such as those described in Goran Stemme, J. Micromech. Microeng., 1(1991) 113-125, a micro-structure having a beam-, bridge-, or diaphragm-like member of thin, flexural material is employed. Such a micro-structure in a resonant sensor is made by applying the production techniques used in the manufacture of semiconductor devices, such as photolithography and etching. Thus, the flexural members may suffer from permanent deformation through the bend and contact thereof with another component of the sensor during the production process of the member, which leads to a failure of the intended sensor, as in the production of capacitors of semiconductor devices described above.
Furthermore, similar micro-structures having a beam-, bridge-, or diaphragm-like member may also be used in various devices called micromachines, and can cause the same problem as in the above-mentioned micro-structures of DRAM semiconductor devices and resonant sensors.